Warum schmeckt uns das Essen nicht, wenn wir es nicht riechen können? Warum hören wir die Stimme unseres Gegenübers besser, wenn wir gleichzeitig die Lippenbewegungen betrachten? Und wie tragen eine veränderte Verarbeitung und Integration sensorischer Reize zu psychischen Erkrankungen bei? Mit diesen und ähnlichen Fragen beschäftigt sich die Forschung zur multisensorischen Integration.

In this viewpoint article, Jennifer Bizley and Daniel Senkowski share their perspectives on past, present, and future developments in research on the roles of functional coupling and neural oscillations in multisensory integration. Drawing on existing studies, the authors argue that a central finding that has shaped the field is that processing in early sensory cortices is influenced by stimuli from other modalities. This finding challenges the classical view of these areas as strictly unisensory. Advances in brain stimulation methods, high-density neural recordings, and computational and machine learning approaches are propelling the field toward richer datasets, a more mechanistic understanding, and causal tests of how neural oscillations and functional coupling may support multisensory integration. Key controversies include the significance of the individual alpha frequency in multisensory integration, and whether crossmodal interactions in early sensory cortices reflect genuine multisensory interactions or movement-related artifacts. The authors advocate for open science practices, including preregistration, data sharing, and publicly available analysis code. Looking ahead, the authors anticipate that the implementation of artificial intelligence and the use of large-scale microelectrode arrays will bridge the gap between micro- and macroscale observations by linking circuit-level findings in animals to large-scale human neuroimaging data. They advise young scientists to develop expertise across multiple sensory modalities, pursue unexpected findings, and actively engage with the collaborative multisensory research community. The authors emphasize that multisensory research examining functional coupling and neural oscillations is ecologically valid, full of unanswered questions, and of growing importance in cognitive and clinical neuroscience.

Observing touch activates similar brain regions as experiencing an actual touch, suggesting that visual information can cross-modally influence tactile perception. This electroencephalography (EEG) study investigated how observing being touched affects the processing and perception of digitally delivered tactile stimuli resembling affective stroking or non-affective tapping. Thirty-three participants received touch patterns on their left forearm via a wearable sleeve while viewing spatiotemporally aligned videos of touch or a photo of an arm. Continuity and pleasantness ratings were higher for stroking than tapping. Correlations between continuity and pleasantness ratings for stroking or tapping conditions were stronger when presented with touch videos than with photos. Analysis of evoked brain activity revealed cross-modal effects after 0.6 seconds at centro-parietal and frontal electrodes for stroking, which differed from the effects observed for tapping. Visual modulation of pleasantness ratings correlated positively with processing differences between stroking and tapping in two right frontal clusters in later time windows around 1.36 and 1.8 s. These results suggest that visual inputs influence tactile pleasantness through somatosensory and multisensory processing, as well as frontal valuation of pleasantness. Our study extends previous research on affective touch by demonstrating informative visual cross-modal influences on digitally actuated touch at behavioural and neural levels. ### Competing Interest Statement The authors have declared no competing interest. Federal Ministry of Research, Technology and Space, 16KISK001K Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64, EXC 2050/1 – 390696704, SE1859/10-1

This study tested whether intersensory attention deficits in people with schizophrenia (SZ) relate to aberrant ongoing oscillations in sensory cortices. Electroencephalography (EEG) was recorded while individuals with schizophrenia (N = 27) and healthy controls (HC; N = 27) performed a visual-tactile target detection task. Ongoing alpha (8–12 Hz) and lower beta (13–20 Hz) band oscillations in visual and sensorimotor cortices were examined. Behavioral data suggested an intersensory attention deficit in patients. EEG data revealed stronger alpha-band oscillations for tactile vs. visual attention conditions in the visual cortex of both study groups. In the sensorimotor cortex contralateral to the tactile stimulation site, patients showed an additional intersensory attention effect in ongoing beta-band oscillations, which was negatively related to cognitive and positive symptoms of the PANSS. Our findings extend previous results from unisensory attention research and suggest that deficits in intersensory attention and alterations in sensorimotor beta oscillations are related to schizophrenia symptomatology.

The phase of alpha oscillations is proposed to reflect perceptual cycles. Yet, human EEG/MEG studies have yielded inconsistent results, perhaps because they used correlative approaches that did not consider causal phase-perception relationships. In a multi-day computational EEG study, we developed the neurobehavioral link function (NBLF) as a new approach to model individual sinusoidal relationships between the alpha phase and multisensory perception and to test for causality. Rhythmic 10 Hz visual stimulation entrained the alpha phase at 0° or 180° relative to audiovisual target onset. Entrainment effects on multisensory integration only emerged when individual NBLFs, which were related to alpha phase coupling between early audio-visual cortices, were included in the analysis. A follow-up psychophysical experiment confirmed individual phase-dependent effects at 5 and 10 Hz, but not 15 Hz. Our results suggest that the individual alpha phase causally modulates perceptual cycles in multisensory integration and advocate for personalized, phase-targeting strategies in neurotechnologies. ### Competing Interest Statement The authors have declared no competing interest. Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64, RO 5587/1-1, RO 5587/5-1, SE1859/10-1

Carrying out any everyday task, be it driving in traffic, conversing with friends or playing basketball, requires rapid selection, integration and segregation of stimuli from different sensory modalities. At present, even the most advanced artificial intelligence-based systems are unable to replicate the multisensory processes that the human brain routinely performs, but how neural circuits in the brain carry out these processes is still not well understood. In this Perspective, we discuss recent findings that shed fresh light on the oscillatory neural mechanisms that mediate multisensory integration (MI), including power modulations, phase resetting, phase-amplitude coupling and dynamic functional connectivity. We then consider studies that also suggest multi-timescale dynamics in intrinsic ongoing neural activity and during stimulus-driven bottom-up and cognitive top-down neural network processing in the context of MI. We propose a new concept of MI that emphasizes the critical role of neural dynamics at multiple timescales within and across brain networks, enabling the simultaneous integration, segregation, hierarchical structuring and selection of information in different time windows. To highlight predictions from our multi-timescale concept of MI, real-world scenarios in which multi-timescale processes may coordinate MI in a flexible and adaptive manner are considered.

Background In recent years, there has been an increasing quest in improving our understanding of neurocognitive deficits underlying adult attention-deficit/hyperactivity disorder (ADHD). Current statistical manuals of psychiatric disorders emphasize inattention and hyperactivity-impulsivity symptoms, but empirical studies have also shown consistent alterations in inhibitory control. Thus far, there is no established neuropsychological test to assess inhibitory control deficits in adult ADHD. A common paradigm for assessing response inhibition is the stop-signal task (SST). Methods Following PRISMA-selection criteria, our systematic review and meta-analysis integrated the findings of 26 publications with 27 studies examining the SST in adult ADHD. Results The meta-analysis, which included 883 patients with adult ADHD and 916 control participants, revealed reliable inhibitory control deficits, as expressed in prolonged SST response times, with a moderate effect size g = 0.51. The deficits were not moderated by study quality, sample characteristics or clinical parameters, suggesting that they may be a phenotype in this disorder. The analyses of secondary outcome measures revealed greater SST omission errors and reduced go accuracy in patients, indicative of altered sustained attention. However, only few (N<10) studies were available for these measures. Discussion Our meta-analysis suggests that the SST could, in conjunction with other tests and questionnaires, become a valuable tool for the assessment of inhibitory control deficits in adult ADHD.

Working memory (WM) is essential for reasoning, decision-making, and problem solving. Recently, there has been an increasing effort in improving WM through noninvasive brain stimulation (NIBS), especially transcranial direct and alternating current stimulation (tDCS/tACS). Studies suggest that tDCS and tACS can modulate WM performance, but large variability in research approaches hinders the identification of optimal stimulation protocols and interpretation of study results. Moreover, it is unclear whether tDCS and tACS differentially affect WM. Here, we summarize and compare studies examining the effects of tDCS and tACS on WM performance in healthy adults. Following PRISMA-selection criteria, our systematic review resulted in 43 studies (29 tDCS, 11 tACS, 3 both) with a total of 1826 adult participants. For tDCS, only 4 out of 23 single-session studies reported effects on WM, while 7 out of 9 multi-session experiments showed positive effects on WM training. For tACS, 10 out of 14 studies demonstrated effects on WM, which were frequency dependent and robust for frontoparietal stimulation. Our review revealed no reliable effect of single-session tDCS on WM but moderate effects of multi-session tDCS and single-session tACS. We discuss the implications of these findings and future directions in the emerging research field of NIBS and WM.

The combination of signals from different sensory modalities can enhance perception and facilitate behavioral responses. While previous research described crossmodal influences in a wide range of tasks, it remains un-clear how such influences drive performance enhancements. In particular, the neural mechanisms underlying performance-relevant crossmodal influences, as well as the latency and spatial profile of such influences are not well understood. Here, we examined data from high-density electroencephalography ( N = 30) recordings to char-acterize the oscillatory signatures of crossmodal facilitation of response speed, as manifested in the speeding of visual responses by concurrent task-irrelevant auditory information. Using a data-driven analysis approach, we found that individual gains in response speed correlated with larger beta power difference (13-25 Hz) between the audiovisual and the visual condition, starting within 80 ms after stimulus onset in the secondary visual cortex and in multisensory association areas in the parietal cortex. In addition, we examined data from electrocorticog-raphy (ECoG) recordings in four epileptic patients in a comparable paradigm. These ECoG data revealed reduced beta power in audiovisual compared with visual trials in the superior temporal gyrus (STG). Collectively, our data suggest that the crossmodal facilitation of response speed is associated with reduced early beta power in mul-tisensory association and secondary visual areas. The reduced early beta power may reflect an auditory-driven feedback signal to improve visual processing through attentional gating. These findings improve our understand-ing of the neural mechanisms underlying crossmodal response speed facilitation and highlight the critical role of beta oscillations in mediating behaviorally relevant multisensory processing.

In the flash-lag illusion (FLI), the position of a flash presented ahead of a moving bar is mislocalized, so the flash appears to lag the bar. Currently, it is not clear whether this effect is due to early perceptual-related neural processes such as motion extrapolation or reentrant processing, or due to later feedback processing relating to postdiction, i.e., retroactively altered perception. We presented 17 participants with the FLI paradigm while recording EEG. A central flash occurred either 51 ms ("early") or 16 ms ("late") before the bar moving from left to right reached the screen center. Participants judged whether the flash appeared to the right ("no flash lag illusion") or to the left ("flash-lag illusion") of the bar. Using single-trial linear modeling, we examined the influence of timing ("early" vs. "late") and perception ("illusion" vs. "no illusion") on flash-evoked brain responses and estimated the cortical sources underlying the FLI. An earlier frontal and occipital component (200-276 ms) differentiated time-locked early vs. late stimulus presentation, indicating that early evoked brain responses reflect feature encoding in the FLI. Perception of the FLI was associated with a late window (368-452 ms) in the ERP, with larger deflections for illusion than no illusion trials, localized to the left inferior occipital gyrus. This suggests a postdiction-related reconstruction of ambiguous sensory stimulation involving late processes in the occipito-temporal cortex, previously associated with temporal integration phenomena. Our findings indicate that perception of the FLI relies on an interplay between ongoing stimulus encoding of the moving bar and feedback processing of the flash, which takes place at later integration stages.

Studies on schizophrenia (SCZ) and aberrant multisensory integration (MSI) show conflicting results, which are potentially confounded by attention deficits in SCZ. To test this, we examined the interplay between MSI and intersensory attention (IA) in healthy controls (HCs) (N = 27) and in SCZ (N = 27). Evoked brain potentials to unisensory-visual (V), unisensory-tactile (T), or spatiotemporally aligned bisensory VT stimuli were measured with high-density electroencephalography, while participants attended blockwise to either visual or tactile inputs. Behaviorally, IA effects in SCZ, relative to HC, were diminished for unisensory stimuli, but not for bisensory stimuli. At the neural level, we observed reduced IA effects for bisensory stimuli over mediofrontal scalp regions (230-320 ms) in SCZ. The analysis of MSI, using the additive approach, revealed multiple phases of integration over occipital and frontal scalp regions (240-364 ms), which did not differ between HC and SCZ. Furthermore, IA and MSI effects were both positively related to the behavioral performance in SCZ, indicating that IA and MSI mutually facilitate bisensory stimulus processing. Multisensory processing could facilitate stimulus processing and compensate for top-down attention deficits in SCZ. Differences in attentional demands, which may be differentially compensated by multisensory processing, could account for previous conflicting findings on MSI in SCZ.

Objectives People with Schizophrenia (SZ) show deficits in auditory and audiovisual speech recognition. It is possible that these deficits are related to aberrant early sensory processing, combined with an impaired ability to utilize visual cues to improve speech recognition. In this electroencephalography study we tested this by having SZ and healthy controls (HC) identify different unisensory auditory and bisensory audiovisual syllables at different auditory noise levels. Methods SZ (N = 24) and HC (N = 21) identified one of three different syllables (/da/, /ga/, /ta/) at three different noise levels (no, low, high). Half the trials were unisensory auditory and the other half provided additional visual input of moving lips. Task-evoked mediofrontal N1 and P2 brain potentials triggered to the onset of the auditory syllables were derived and related to behavioral performance. Results In comparison to HC, SZ showed speech recognition deficits for unisensory and bisensory stimuli. These deficits were primarily found in the no noise condition. Paralleling these observations, reduced N1 amplitudes to unisensory and bisensory stimuli in SZ were found in the no noise condition. In HC the N1 amplitudes were positively related to the speech recognition performance, whereas no such relationships were found in SZ. Moreover, no group differences in multisensory speech recognition benefits and N1 suppression effects for bisensory stimuli were observed. Conclusion Our study shows that reduced N1 amplitudes relate to auditory and audiovisual speech processing deficits in SZ. The findings that the amplitude effects were confined to salient speech stimuli and the attenuated relationship with behavioral performance, compared to HC, indicates a diminished decoding of the auditory speech signals in SZs. Our study also revealed intact multisensory benefits in SZs, which indicates that the observed auditory and audiovisual speech recognition deficits were primarily related to aberrant auditory speech processing. Highlights Speech processing deficits in schizophrenia related to reduced N1 amplitudes Audiovisual suppression effect in N1 preserved in schizophrenia Schizophrenia showed weakened P2 components in specifically audiovisual processing

Studies on schizophrenia (SCZ) and aberrant multisensory integration (MSI) show conflicting results. These divergent results are potentially confounded by attention deficits in SCZ. To test this, we examined the interplay between MSI and intersensory attention (IA) in healthy controls (N=27) and in SCZ (N=27). Evoked brain potentials to unisensory-visual (V), unisensory-tactile (T) or bisensory VT stimuli were measured with high density electroencephalography, whilst participants attended block-wise to either visual or tactile inputs. Behaviourally, IA effects in SCZ are uncompromised for bisensory stimuli, but diminished for unisensory stimuli. At the neural level, we observed reduced IA effects for bisensory stimuli over mediofrontal scalp regions (230-320ms) in SCZ. The analysis of MSI revealed multiple phases of integration over occipital and frontal scalp regions (240-364ms), with comparable performance between HC and SCZ. The magnitudes of IA and MSI effects were both positively related to the behavioural performance in SCZ, indicating that IA and MSI mutually facilitate bisensory stimulus processing. Our study suggests that widely intact MSI, which facilitates stimulus processing, can compensate for top-down attention deficits in SCZ. Further, the interplay of IA and MSI implies that differences in attentional demands may account for previous conflicting findings on MSI in schizophrenia.### Competing Interest StatementThe authors have declared no competing interest.

Patients with schizophrenia (ScZ) often show impairments in auditory information processing. These impairments have been related to clinical symptoms, such as auditory hallucinations. Some researchers have hypothesized that aberrant low-frequency oscillations contribute to auditory information processing deficits in ScZ. A paradigm for which modulations in low-frequency oscillations are consistently found in healthy individuals is the auditory continuity illusion (ACI), in which restoration processes lead to a perceptual grouping of tone fragments and a mask, so that a physically interrupted sound is perceived as continuous. We used the ACI paradigm to test the hypothesis that low-frequency oscillations play a role in aberrant auditory information processing in patients with ScZ (N = 23). Compared with healthy control participants we found that patients with ScZ show elevated continuity illusions of interrupted, partially-masked tones. Electroencephalography data demonstrate that this elevated continuity perception is reflected by diminished 3 Hz power. This suggests that reduced low-frequency oscillations relate to elevated restoration processes in ScZ. Our findings support the hypothesis that aberrant low-frequency oscillations contribute to altered perception-related auditory information processing in ScZ.

Integrating information across different senses is a central feature of human perception. Previous research suggests that multisensory integration is shaped by a context-dependent and largely adaptive interplay between stimulus-driven bottom-up and top-down endogenous influences. One critical question concerns the extent to which this interplay is sensitive to the amount of available cognitive resources. In the present study, we investigated the influence of limited cognitive resources on audiovisual integration by measuring high-density electroencephalography (EEG) in healthy participants performing the sound-induced flash illusion (SIFI) and a verbal n-back task (0-back, low load and 2-back, high load) in a dual-task design. In the SIFI, the integration of a flash with two rapid beeps can induce the illusory perception of two flashes. We found that high compared with low load increased illusion susceptibility and modulated neural oscillations underlying illusion-related crossmodal interactions. Illusion perception under high load was associated with reduced early β power (18–26 Hz, ∼70 ms) in auditory and motor areas, presumably reflecting an early mismatch signal and subsequent top-down influences including increased frontal θ power (7–9 Hz, ∼120 ms) in mid-anterior cingulate cortex (ACC) and a later β power suppression (13–22 Hz, ∼350 ms) in prefrontal and auditory cortex. Our study demonstrates that integrative crossmodal interactions underlying the SIFI are sensitive to the amount of available cognitive resources and that multisensory integration engages top-down θ and β oscillations when cognitive resources are scarce. SIGNIFICANCE STATEMENT The integration of information across multiple senses, a remarkable ability of our perceptual system, is influenced by multiple context-related factors, the role of which is highly debated. It is, for instance, poorly understood how available cognitive resources influence crossmodal interactions during multisensory integration. We addressed this question using the sound-induced flash illusion (SIFI), a phenomenon in which the integration of two rapid beeps together with a flash induces the illusion of a second flash. Replicating our previous work, we demonstrate that depletion of cognitive resources through a working memory (WM) task increases the perception of the illusion. With respect to the underlying neural processes, we show that when available resources are limited, multisensory integration engages top-down θ and β oscillations.